1. Field of the Invention
The present invention relates to a variable matching circuit that uses a variable-capacitance capacitor having a dielectric layer whose dielectric constant changes depending on an applied voltage, and that is capable of making an impedance variable according to a capacitance change, as a matching circuit used in communication equipments such as mobile phones and high-frequency components installed in the communication equipments, and in particular, relates to a variable matching circuit that has excellent characteristics, for example, that is excellent in electric high power handling capability, low-distortion, and low-loss.
The present invention relates to a variable resonance circuit that uses a variable-capacitance capacitor having a dielectric layer whose dielectric constant changes depending on an applied voltage, and that is capable of making a resonance frequency variable according to a capacitance change, as a resonance circuit used in communication equipments such as mobile phones and high-frequency components installed in the communication equipments, and in particular, relates to a variable resonance circuit that has excellent characteristics, for example, that is excellent in electric high power handling capability, low-distortion, and low-loss.
The invention relates to a variable phase-shifting circuit that uses a variable-capacitance capacitor having a dielectric layer whose dielectric constant changes depending on an applied voltage and being capable of changing capacitance, and that is capable of changing a phase-shifting amount according to a capacitance change, as a phase-shifting circuit used in communication equipments of microwave bands and millimeter-wave bands and high-frequency components of phased array antennas, amplifiers and the like, and in particular, relates to a variable phase-shifting circuit that has excellent characteristics, for example, that is excellent in electric high power handling capability, low-distortion, and low-loss.
The invention relates to a variable attenuation circuit that uses a variable-capacitance capacitor having a dielectric layer whose dielectric constant changes depending on an applied voltage and being capable of changing capacitance, and that is capable of changing an attenuation amount according to a capacitance change, as an attenuation circuit used in communication equipments of microwave bands and millimeter-wave bands and high-frequency components of variable beam antennas, amplifiers and the like and attenuating signals, and in particular, relates to a variable attenuation circuit that has excellent characteristics, for example, that is excellent in electric high power handling capability, low-distortion, and easy to operate.
2. Description of the Related Art
In general, high-frequency components are designed to have input/output impedances of 50Ω, and characteristics thereof are evaluated and guaranteed by a measurement system having a load impedance of 50Ω. However, actually, the input/output impedances of the high-frequency components deviate from 50Ω because of variations of used circuit components and wiring patterns Therefore, for example, in the case of designing communication equipment using a plurality of high-frequency components, the high-frequency components are designed to have input/output impedances of 50Ω, but there is a problem such that mismatching of the impedances occurs because of deviation of the input/output impedances of the high-frequency components from 50Ω, or because of variations of the dimensions of the wiring patterns, interference and so on, and consequently, a characteristic desired for the communication equipment may not be obtained.
Accordingly, in order to control mismatching of the impedances among the high-frequency components, a countermeasure of, for example, using a matching circuit composed of impedance devices including a capacitor, a resistor, an inductor and a transmission line and replacing the impedance devices one by one is taken, whereby the impedances are regulated, and the desired characteristic is obtained.
Further, in the same way, when designing the high-frequency components, in order to obtain the desired characteristic, it is common to design on the assumption that the countermeasure of using a matching circuit composed of impedance devices including a capacitor, a resistor, an inductor and a transmission line and replacing the impedance devices one by one is taken to regulate the impedances and obtain the desired characteristic.
On the other hand, in the case of actually using mobile communication equipment such as a mobile terminal regulated so as to have a desired characteristic, there arises a problem such that an electromagnetic field in the communication equipment is disturbed under the influence of a human body holding the communication equipment when using, impedance mismatching occurs, and communication is hindered by deterioration in receiving sensitivity.
In order to solve these problems, a variable matching circuit made by combining impedance devices including a capacitor, a resistor, an inductor and a transmission line, and a variable-capacitance diode has been known since before.
Further, a variable matching circuit made by using a variable-capacitance capacitor instead of the variable-capacitance diode has been proposed (refer to Japanese Unexamined Patent Publications JP-A 10-335980 (1998) and JP-A 11-111566 (1999), for example).
However, the variable matching circuit using the variable-capacitance diode has a problem such that the variable matching circuit can be used only in a receiving apparatus and a receiving circuit that need small operation power, because the electric high power handling capability of the variable-capacitance diode is low and a distortion characteristic due to the nonlinearity of capacitance is large. In other words, there is a problem such that the variable matching circuit cannot be used in a transmission apparatus or a transmission circuit that need large operation power. Additionally, the variable matching circuit has a problem such that loss at a high frequency is large.
Further, in the variable matching circuit using the variable-capacitance capacitor as proposed in JP-A 10-335980 and JP-A 11-111566, a capacitance change of the variable-capacitance capacitor is caused also by a high-frequency voltage, so that the variable matching circuit has a problem such that distortion characteristics such as waveform distortion and intermodulation distortion become large when the high-frequency voltage is high. Moreover, in order to make the distortion characteristics small, it is necessary to decrease the high-frequency electric field strength of the variable-capacitance capacitor and reduce the capacitance change by the high-frequency voltage. It is effective therefor to increase the thickness of a dielectric layer. However, there is a problem such that direct current electric field strength is also decreased when the thickness of the dielectric layer is increased, and therefore, a capacitance change rate is also decreased, and an impedance control width in the variable matching circuit becomes small.
Further, since an electric current easily flows to the variable-capacitance capacitor in a case of high-frequency signals, there is a problem such that the variable-capacitance capacitor generates heat and breaks down because of loss resistance while the variable-capacitance capacitor is used in a high-frequency circuit, and therefore, the electric high power handling capability of the variable matching circuit against the high-frequency signals is low. It is effective also for the problem of the electric high power handling capability to increase the thickness of the dielectric layer and decrease a heat generation amount per unit volume. However, there is a problem such that the direct current electric field strength is also decreased when the thickness of the dielectric layer is increased, and therefore, a capacitance change rate is also decreased, and an impedance control width in the variable matching circuit becomes small.
Furthermore, as shown in an equivalent circuit view of FIG. 19, bias signals are supplied from a bias terminal V via a bias supply circuit G to a variable-capacitance diode 201, so that the independent bias supply circuit G formed by a choke coil L2 is necessary in the variable matching circuit. Therefore there is a problem such that it is necessary to design the bias supply circuit G separately from the variable matching circuit, it takes time for regulation thereof. Moreover, there is a problem such that the circuit becomes large-sized as a whole because the variable matching circuit and the bias supply circuit G are separately formed. The same problem occurs even if the variable-capacitance diode is replaced with a variable-capacitance capacitor.
Still further, there is a problem such that the variable-capacitance diode 201 has a polarity for an applied voltage, and therefore, it is required to pay attention to the polarity not only when designing but also when mounting, and it takes time for mounting.
Furthermore, a variable resonance circuit made by combining impedance devices including inductor components such as an inductor and a transmission liner and a variable-capacitance diode has been known since before, and has been used as a resonance circuit of a voltage controlled oscillator, a voltage controlled variable filter, and a notch circuit for eliminating unnecessary harmonics components and noise components.
However, the conventional variable resonance circuit using the variable-capacitance diode has a problem such that loss at a high frequency is large in the variable-capacitance diode, and therefore, loss in the entire resonance circuit becomes large, and a resonance characteristic is deteriorated. For example, in the case of using the resonance circuit in the filter, there is a problem such that selectivity, a passing characteristic, an attenuation characteristic and so on are deteriorated by deterioration in a resonance waveform at a resonance frequency. Moreover, in the case of using the resonance circuit in the oscillator, there is a problem such that the C/N and S/N of the oscillator are deteriorated.
Still further, the conventional variable resonance circuit using the variable-capacitance diode has a problem such that the variable resonance circuit can be used only in a receiving apparatus and a receiving circuit that need small operation power, because the electric high power handling capability of the variable-capacitance diode is low and a distortion characteristic due to the nonlinearity of capacitance is large. In other words, there is a problem such that the variable matching circuit cannot be used in a transmission apparatus or a transmission circuit that need large operation power.
Further, in the conventional variable resonance circuit using the variable-capacitance capacitor as proposed in Japanese Unexamined Patent Publication JP-A 10-335903 (1998), a capacitance change of the variable-capacitance capacitor is caused also by a high-frequency voltage, so that the variable resonance circuit has a problem such that distortion characteristics such as waveform distortion and intermodulation distortion become large when the high-frequency voltage is high. Moreover, in order to make the distortion characteristics small, it is necessary to decrease the high-frequency electric field strength of the variable-capacitance capacitor and reduce the capacitance change by the high-frequency voltage. It is effective therefor to increase the thickness of a dielectric layer. However, there is a problem such that direct current electric field strength is also decreased when the thickness of the dielectric layer is increased, and therefore, a capacitance change rate is also decreased, and a resonance frequency variable width in the variable resonance circuit becomes small.
Further, since an electric current easily flows to the variable-capacitance capacitor in a case of high-frequency signals, there is a problem such that the variable-capacitance capacitor generates heat and breaks down because of loss resistance while the variable-capacitance capacitor is used in a high-frequency circuit, and therefore, the electric high power handling capability of the variable resonance circuit is low. It is effective also for the problem of the electric high power handling capability to increase the thickness of the dielectric layer and decrease a heat generation amount per unit volume. However, there is a problem such that the direct current electric field strength is also decreased when the thickness of the dielectric layer is increased, and therefore, a capacitance change rate is also decreased, and a resonance frequency variable width in the variable resonance circuit becomes small.
Furthermore, in the variable resonance circuit using the variable-capacitance diode, as shown in an equivalent circuit view of FIG. 20, bias signals are supplied from bias terminals V1 and V2 via a bias supply circuit G to a variable-capacitance diode 201, so that the independent bias supply circuit G formed by choke coils L2 and L3 is necessary in the variable resonance circuit. Therefore, there is a problem such that it is necessary to design the bias supply circuit G, it takes time for regulation thereof. Moreover, there is a problem such that the circuit becomes large-sized as a whole because the variable resonance circuit and the bias supply circuit G are separately formed. With respect to the need for the bias supply circuit G, the conventional variable resonance circuit has the same problem even if the variable-capacitance diode is replaced with a variable-capacitance capacitor.
Still further, the variable resonance circuit using the variable-capacitance diode also has a problem such that the variable-capacitance diode 201 has a polarity for an applied voltage, and therefore, it is required to pay attention to the polarity not only when designing but also when mounting, and it takes time for mounting.
Furthermore, a variable phase-shifting circuit made by combining a transmission line, a circulator and a variable-capacitance diode has been known since before, and has been used as a phase-shifting circuit for beam control of a phased-array antenna, for an amplifier and the like.
Further, a variable phase-shifting circuit made by using a voltage control type of dielectric varactor instead of a variable-capacitance diode, and combining the varactor as a reflective terminal portion with a rat-race coupler or placing the voltage control type of dielectric varactor within a stub in a radius direction extending from a microstrip line has been proposed (refer to Japanese Unexamined Patent Publication based on International Application JP-A 2002-528899, for example). The voltage control type of dielectric varactor is composed of a substrate having a first dielectric constant and having an almost flat surface, a controllable ferroelectric layer having a second dielectric constant larger than the first dielectric constant and disposed on the almost flat surface of the substrate, and first and second electrodes disposed on a surface of the controllable ferroelectric layer opposite to the almost flat surface of the substrate, the first and second electrodes are separated so as to form a gap therebetween. The voltage control type of dielectric varactor corresponds to a variable-capacitance capacitor.
However, the conventional variable phase-shifting circuit using the variable-capacitance diode has a problem such that loss at a high frequency is large in the variable-capacitance diode, and therefore, loss in the entire phase-shifting circuit becomes large is deteriorated.
However, the variable phase-shifting circuit using the variable-capacitance diode has a problem such that the variable phase-shifting circuit can be used only in a receiving apparatus and a receiving circuit that need small operation power, because the electric high power handling capability of the variable-capacitance diode is low and a distortion characteristic due to the nonlinearity of capacitance is large. In other words, there is a problem such that the variable matching circuit cannot be used in a transmission apparatus or a transmission circuit that need large operation power.
Furthermore, in the variable phase-shifting circuit using the variable-capacitance diode, as shown in an equivalent circuit view of FIG. 21, bias signals are supplied from a bias terminal V via a bias supply circuit G to variable-capacitance diodes 201 and 202, so that the independent bias supply circuit G formed by choke coils L1 and L2 is necessary in the variable phase-shifting circuit. Therefore, there is a problem such that it is necessary to design the bias supply circuit G separately from the variable phase-shifting circuit, it takes time for regulation thereof. Moreover, there is a problem such that the circuit becomes large-sized as a whole because the variable phase-shifting circuit and the bias supply circuit G are separately formed. The same problem occurs even if the variable-capacitance diode is replaced with a variable-capacitance capacitor.
Still further, in the variable phase-shifting circuit using the variable-capacitance diode, there is a problem such that the variable-capacitance diode 201 and 202 has a polarity for an applied voltage, and therefore, it is required to pay attention to the polarity not only when designing but also when mounting, and it takes time for mounting.
Further, in the conventional variable phase-shifting circuit using the voltage control type of dielectric varactor as proposed in JP-A 2002-528899, a capacitance change of the voltage control type of dielectric varactor (i.e., the variable-capacitance capacitor) is caused also by a high-frequency voltage, so that the variable phase-shifting circuit has a problem such that distortion characteristics such as waveform distortion and intermodulation distortion become large when the high-frequency voltage is high. Moreover, in order to make the distortion characteristics small, it is necessary to decrease the high-frequency electric field strength of the variable-capacitance capacitor and reduce the capacitance change by the high-frequency voltage. It is effective therefor to increase the gap of a capacitance forming portion. However, there is a problem such that direct current electric field strength is also decreased when the gap of a capacitance forming portion is increased, and therefore, a capacitance change rate is also decreased, and a variable width of the phase-shifting amount in the variable phase-shifting circuit becomes small.
Further, since an electric current easily flows to the variable-capacitance capacitor in a case of high-frequency signals, there is a problem such that the variable-capacitance capacitor generates heat and breaks down because of loss resistance while the variable-capacitance capacitor is used in a high-frequency circuit, and therefore, the electric high power handling capability of the variable phase-shifting circuit is low. It is effective also for the problem of the electric high power handling capability to increase the gap of the capacitance forming portion (i.e., to increase the thickness of the dielectric layer) and decrease a heat generation amount per unit volume. However, there is a problem such that the direct current electric field strength is also decreased when the gap of a capacitance forming portion is increased (i.e., the thickness of the dielectric layer is increased), and therefore, a capacitance change rate is also decreased, and variable width of the phase-shifting amount in the variable phase-shifting circuit becomes small.
Furthermore, since before, a variable attenuation circuit that is made by combining a distributor for distributing signals to a plurality of paths, a synthesizer for synthesizing the signals passed through the plurality of paths, and a variable-capacitance diode, that counteracts the signals according to the phase difference of the distributed signals of the respective paths, and that attenuates the signals has been known (refer to Japanese Unexamined Patent Publication JP-A 6-177694 (1994), for example).
However, the conventional variable attenuation circuit using the variable-capacitance diode has a problem such that the electric high power handling capability of the variable-capacitance diode is low and a distortion characteristic due to the nonlinearity of capacitance is large.
Further, in the conventional variable attenuation circuit using the variable-capacitance diode, loss at a high frequency in the variable-capacitance diode is large, and therefore, for example, in a case where the variable attenuation circuit is used in a receiving circuit, the level of a reception signal is small, and there arises a problem such that a signal is attenuated when attenuation of the signal is not desired.
Furthermore, in the variable attenuation circuit using the variable-capacitance diode, as shown in an equivalent circuit view of FIG. 22, bias signals are supplied from a bias terminal V via a bias supply circuit G to a variable-capacitance diode 201, so that the independent bias supply circuit G formed by choke coils L1 and L2 is necessary in the variable attenuation circuit. Therefore, there is a problem such that it is necessary to design the bias supply circuit G, it takes time for regulation thereof. Moreover, there is a problem such that the circuit becomes large-sized as a whole because the variable attenuation circuit and the bias supply circuit G are separately formed.
Still further, in the variable attenuation circuit using the variable-capacitance diode, there is a problem such that the variable-capacitance diode 201 has a polarity for an applied voltage, and therefore, it is required to pay attention to the polarity not only when designing but also when mounting, and it takes time for mounting.
In FIG. 22, reference numerals T11, T12, T13, T21, T22 and T23 denote λ/4 transmission lines, reference numerals R101 and R102 denote resistors, reference numerals C101 and C102 denote direct current restriction capacitance devices, reference symbol I denotes an input signal terminal, and reference symbol O denotes an output signal terminal.